1. Field of the Invention
This invention relates generally to a sewing machine wherein the position of a workpiece relative to a needle is controlled in accordance with stitch instructions which determine the position of two or more successive stitches constituting a specific unit stitch pattern to form a series of such unit stitch patterns on the workpiece along a predetermined reference line, and more particularly to an automatic programming system for automatically working out the stitch instructions for the sewing machine.
2. Description of the Prior Art
There have been developed various sorts of sewing machines capable of forming on a workpiece a complicated seam including a considerable number of stitches. On such sewing machines, stitch instructions specifying or determining each stitch position are extracted sequentially from a data memory to control relative position between the workpiece and the needle and thus the sewing operation may be efficiently performed along a desired line corresponding to the seam. For example, a secondary workpiece may be neatly and accurately sewn on a primary workpiece by successively forming a preselected unit stitch pattern having two or more stitches along the periphery of the secondary workpiece.
Keeping up with the developments of such sewing machines, a variety of automatic programming systems have been developed for automatically preparing stitch instructions necessary for such sewing machines to be able to form successive stitches of a specific unit pattern along a desired stitching line. In those programming systems, the position data representing each stitch position on a desired line (a line corresponding to a seam, constituted by successive stitches) is either worked out for each stitch position manually by a machine operator, or determined by tracing step by step, through a manual operating means, a profile drawn on a record medium as a desired line, and calculating a distance traced in each step from one stitch position to another. For instance, in the U.S. patent of Takao Manabe, U.S. Pat. No. 4,116,143, there is shown a programming system wherein a sewing pattern sheet is provided with marks corresponding to needle lowering positions of a predetermined sewing profile, and the data representing the position of a selected mark is stored in a memory device through operation of a manual operating means by a machine operator when a stylus is positioned on the selected mark. This manual operation will be more cumbersome for the operator and more difficult to perform, and consequently the operator will need more programming time for working out and storing the position data of the marks as the predetermined sewing profile becomes more complicated and the number of the marks is increased. This disadvantage of the system disclosed in the above patent specification means that there are not a few chances for the operator to make programming errors. Thus, the conventionally available programming systems are considerably low in programming efficiency.